Return to KLUBNL.PL main page
| To: | [email protected] |
|---|---|
| Subject: | Re: LF: Related Technical Query - Soundcard calibrator |
| From: | "Stewart Nelson" <[email protected]> |
| Date: | Fri, 12 Dec 2003 06:54:21 -0800 |
| References: | <000001c3c0a1$86f819e0$fce8c593@rsch15> |
| Reply-to: | [email protected] |
| Sender: | <[email protected]> |
|
Hi Andy and all,
I was unaware of H&H, but my previous post gave the same
answer. It was based
on my naive analysis that white noise was spread evenly from 0
to fs/2,
and that the sin(x)/x effect should not affect low
frequencies.
When I saw Stewart Bryant's post, it seemed that there really
needed to be
a PI in there, so I shut up. Now I'm not so
sure.
I used Cool Edit to generate 1 second of white noise at 48
kHz.
Passed it through a script that changed positive values to 8
samples of
+1/2 full scale, and negative values to 8 samples of
-1/2. This is a
rough approximation to a shift register clocked at 6
kHz.
A small piece of the wave looks like this.
The RMS power reported is -6.02 dB, much as one would
expect.
The frequency analysis plot looks like this:
Then, I did a low pass filter at 100 Hz. The RMS power
now displays as -20.95 dB.
This agrees fairly well with the naive -6.02+10*log(100/3000)
= -20.79 dB,
and appears to support the "no pi" theory.
Unfortunately, I can't explain where the pi went
:(
73,
Stewart KK7KA
----- Original Message -----
From: "James Moritz" <[email protected]>
To: <[email protected]>
Sent: Friday, December 12, 2003 3:17 AM
Subject: RE: LF: Related Technical Query - Soundcard
calibrator
> > I hate to throw a spanner in the works, but... A noise source of exactly > this type is discussed in Horowitz & Hill "The Art of Electronics" 2nd > ed., section 9.34. This gives the formula (in the form Andy has used) > Vrms^2 = Vpk^2 * 2 * BW /Fclock, (giving 224mV rms) which is different > by a factor of sqrt(pi) from the value Andy gets. I spent some time last > night trying to figure out which one is correct, and came out with a > reasonably convincing case for Horowitz & Hill's formula - if anyone is > interested, I will put it into an e-mail compatible form > > > Cheers, Jim Moritz > 73 de M0BMU
|
| Previous by Date: | Re: LF: Soundcard bandpass filter?, DL4YHF |
|---|---|
| Next by Date: | LF: Off Topic---ADSL Analysis s/w, Brian Rogerson |
| Previous by Thread: | RE: LF: Related Technical Query - Soundcard calibrator, James Moritz |
| Next by Thread: | RE: LF: Related Technical Query - Soundcard calibrator, Andy talbot |
| Indexes: | [Date] [Thread] [Top] [All Lists] |
